The connection between abnormal protein phosphorylation and the cause or consequence of diseases has been known for over 20 years. Accordingly, protein kinases have become a very important group of drug targets. See Cohen, Nature, 1:309-315 (2002). Various protein kinase inhibitors have been used clinically in the treatment of a wide variety of diseases, such as cancer and chronic inflammatory diseases, including diabetes and stroke. See Cohen, Eur. J. Biochem., 268:5001-5010 (2001), Protein Kinase Inhibitors for the Treatment of Disease: The Promise and the Problems, Handbook of Experimental Pharmacology, Springer Berlin Heidelberg, 167 (2005).
The protein kinases are a large and diverse family of enzymes that catalyze protein phosphorylation and play a critical role in cellular signaling. Protein kinases may exert positive or negative regulatory effects, depending upon their target protein. Protein kinases are involved in specific signaling pathways which regulate cell functions such as, but not limited to, metabolism, cell cycle progression, cell adhesion, vascular function, apoptosis, and angiogenesis. Malfunctions of cellular signaling have been associated with many diseases, the most characterized of which include cancer and diabetes. The regulation of signal transduction by cytokines and the association of signal molecules with protooncogenes and tumor suppressor genes have been well documented. Similarly, the connection between diabetes and related conditions, and deregulated levels of protein kinases, has been demonstrated. See e.g., Sridhar et al. Pharmaceutical Research, 17(11):1345-1353 (2000). Viral infections and the conditions related thereto have also been associated with the regulation of protein kinases. Park et al. Cell 101 (7): 777-787 (2000).
Because protein kinases regulate nearly every cellular process, including metabolism, cell proliferation, cell differentiation, and cell survival, they are attractive targets for therapeutic intervention for various disease states. For example, cell-cycle control and angiogenesis, in which protein kinases play a pivotal role are cellular processes associated with numerous disease conditions such as but not limited to cancer, inflammatory diseases, abnormal angiogenesis and diseases related thereto, atherosclerosis, macular degeneration, diabetes, obesity, and pain.
Protein kinases have become attractive targets for the treatment of cancers. Fabbro et al., Pharmacology & Therapeutics 93:79-98 (2002). It has been proposed that the involvement of protein kinases in the development of human malignancies may occur by: (1) genomic rearrangements (e.g., BCR-ABL in chronic myelogenous leukemia), (2) mutations leading to constitutively active kinase activity, such as acute myelogenous leukemia and gastrointestinal tumors, (3) deregulation of kinase activity by activation of oncogenes or loss of tumor suppressor functions, such as in cancers with oncogenic RAS, (4) deregulation of kinase activity by over-expression, as in the case of EGFR and (5) ectopic expression of growth factors that can contribute to the development and maintenance of the neoplastic phenotype. Fabbro et al., Pharmacology & Therapeutics 93:79-98 (2002).
The elucidation of the intricacy of protein kinase pathways and the complexity of the relationship and interaction among and between the various protein kinases and kinase pathways highlights the importance of developing pharmaceutical agents capable of acting as protein kinase modulators, regulators or inhibitors that have beneficial activity on multiple kinases or multiple kinase pathways. Accordingly, there remains a need for new kinase modulators.
The protein named mTOR (mammalian target of rapamycin), which is also called FRAP, RAFTI or RAPTI), is a 2549-amino acid Ser/Thr protein kinase, that has been shown to be one of the most critical proteins in the mTOR/PI3K/Akt pathway that regulates cell growth and proliferation. Georgakis and Younes Expert Rev. Anticancer Ther. 6(1):131-140 (2006). mTOR exists within two complexes, mTORC1 and mTORC2. While mTORC1 is sensitive to rapamycin analogs (such as temsirolimus or everolimus), mTORC2 is largely rapamycin-insensitive. Notably, rapamycin is not a TOR kinase inhibitor. Several mTOR inhibitors have been or are being evaluated in clinical trials for the treatment of cancer. Temsirolimus was approved for use in renal cell carcinoma in 2007 and sirolimus was approved in 1999 for the prophylaxis of renal transplant rejection. Everolimus was approved in 2009 for renal cell carcinoma patients that have progressed on vascular endothelial growth factor receptor inhibitors, in 2010 for subependymal giant cell astrocytoma (SEGA) associated with tuberous sclerosis (TS) in patients who require therapy but are not candidates for surgical resection, and in 2011 for progressive neuroendocrine tumors of pancreatic origin (PNET) in patients with unresectable, locally advanced or metastatic disease. There remains a need for additional TOR kinase inhibitors.
DNA-dependent protein kinase (DNA-PK) is a serine/threonine kinase involved in the repair of DNA double strand breaks (DSBs). DSBs are considered to be the most lethal DNA lesion and occur endogenously or in response to ionizing radiation and chemotherapeutics (for review see Jackson, S. P., Bartek, J. The DNA-damage response in human biology and disease. Nature Rev 2009; 461:1071-1078). If left unrepaired, DSBs will lead to cell cycle arrest and/or cell death (Hoeijmakers, J. H. J. Genome maintenance mechanisms for preventing cancer. Nature 2001; 411: 366-374; van Gent, D. C., Hoeijmakers, J. H., Kanaar, R. Chromosomal stability and the DNA double-stranded break connection. Nat Rev Genet 2001; 2: 196-206). In response to the insult, cells have developed complex mechanisms to repair such breaks and these mechanisms may form the basis of therapeutic resistance. There are two major pathways used to repair DSBs, non-homologous end joining (NHEJ) and homologous recombination (HR). NHEJ brings broken ends of the DNA together and rejoins them without reference to a second template (Collis, S. J., DeWeese, T. L., Jeggo P. A., Parker, A. R. The life and death of DNA-PK. Oncogene 2005; 24: 949-961). In contrast, HR is dependent on the proximity of the sister chromatid which provides a template to mediate faithful repair (Takata, M., Sasaki, M. S., Sonoda, E., Morrison, C., Hashimoto, M., Utsumi, H., et al. Homologous recombination and non-homologous end-joining pathways of DNA double-strand break repair have overlapping roles in the maintenance of chromosomal integrity in vertebrate cells. EMBO J 1998; 17: 5497-5508; Haber, J. E. Partners and pathways repairing a double-strand break. Trends Genet 2000; 16: 259-264). NHEJ repairs the majority of DSBs. In NHEJ, DSBs are recognized by the Ku protein that binds and then activates the catalytic subunit of DNA-PK. This leads to recruitment and activation of end-processing enzymes, polymerases and DNA ligase IV (Collis, S. J., DeWeese, T. L., Jeggo P. A., Parker, A. R. The life and death of DNA-PK. Oncogene 2005; 24: 949-961). NHEJ is primarily controlled by DNA-PK and thus inhibition of DNA-PK is an attractive approach to modulating the repair response to exogenously induced DSBs. Cells deficient in components of the NHEJ pathway are defective in DSB repair and highly sensitive to ionizing radiation and topoisomerase poisons (reviewed by Smith, G. C. M., Jackson, S. P. The DNA-dependent protein kinase. Genes Dev 1999; 13: 916-934; Jeggo, P. A., Caldecott, K., Pidsley, S., Banks, G. R. Sensitivity of Chinese hamster ovary mutants defective in DNA double strand break repair to topoisomerase II inhibitors. Cancer Res 1989; 49: 7057-7063). A DNA-PK inhibitor has been reported to have the same effect of sensitizing cancer cells to therapeutically induced DSBs (Smith, G. C. M., Jackson, S. P. The DNA-dependent protein kinase. Genes Dev 1999; 13: 916-934).
Citation or identification of any reference in Section 2 of this application is not to be construed as an admission that the reference is prior art to the present application.